Many types of nuclear reactors heat water in pressure vessels, for power production. General information in regard thereto is disclosed by D. M. Considine in Energy Technology Handbook (McGraw-Hill, 1977).
Below the pressure vessel in many reactors, there is a chamber in which reactor equipment is installed, replaced, and maintained, and other servicing operations are performed. In the undervessel region of the reactor, there are various reactor support structures, including a floor or basemat and a foundation. One or more tunnels extend through the walls of the foundation to permit the entry of personnel and of servicing vehicles travelling on rails.
The servicing vehicles travel onto a platform in the undervessel chamber. The platform, according to the prior art, is rotatable but fixed at a selected elevational level. This permits some servicing operations to be conducted by positioning the servicing tool vehicle directly under the part of the reactor vessel being serviced. Other servicing operations may be very difficult to perform, because the servicing would require the platform to be elevated to a specific level necessary for the work to be accomplished. Different levels may be required for servicing such diverse equipment as control rod drives, core power level monitors, and core circulation pumps.